Scanning antenna



Oct. 24, 1950 H. lAMs 2,527,222

scANNING ANTENNA Filed Oct. 30, 1947 Har Patented Oct. 24, 1950 SCANN ING ANTENNA Harley Iams, Venice, Calif., assignor to Radio Corporation of America, a corporation of Dela- Ware Application October 30, 1947, Serial No. 783,104

(Cl. Z50-33.63)

Claims. l

This invention relates to scanning antennas, for producing a directional beam of radio energy and sweeping said beam cyclically through a predetermined sector. For some purposes, it is desirable to scan sawtooth fashion, i. e., start the beam at one extremity of its scan, move it continuously at constant angular velocity to the other extreme, then return it immediately to the starting position. With scanning of this type, a graph of angular position of the beam against time looks like a sawtooth wave.

The principal object of the present invention is to provide improved means for scanning in the above described manner, wherein no reciprocatory or discontinuous mechanical motions are required.

Another object is to provide a beam scanning structure adaptable for use in conjunction with another scanning device operating at a right angle thereto, to scan in two orthogonal coordinates, such as azimuth and elevation.

The invention will be described with reference to the accompanying drawing, wherein:

Figure 1 is a pictorial view of a scanning antenna system embodying the invention, and

Figure 2 is a plan view of the structure of Fig. 1, with the upper portion removed to show the internal details.

The antenna system illustrated comprises three elements: a radiator I, a scanning rotor assembly 3, and a focusing device 5. In the present example, the radiator I is a flared horn, and the focusing device 5 is a dielectric lens. The scanning rotor comprises four similar stacks 1, 9, I I and I3 of parallel metal plates or ns I5. The stacks 1, 9, II, and I3 of met-al plates I5 may also be considered as four groups of parallel conductive sheets. The fins I5 are all of approximately the same dimensions, and are supported on edge between two discs I1 and I9. The four stacks 1, 9, I I, I3 are spaced at equal angular intervals around the discs in a cross shaped formation.

The upper disc I1 (not shown in Fig. 2) includes a central opening 2l through which a wave guide 23 extends to the horn I. The lower` disc I9 is supported on a shaft 25 which is coupled to a motor 21. Means are thus provided to support the groups of plates 1, 9, II, and I3 for rotation around the radiator I to pass in succession across the beam of the radiator. The wave guide 23 and the radiator I are positioned so that in the normal mode of propagation, the electric vector lies. in a plane perpendicular to the planes of the fins I5, i, e., horizontal in the structure of Fig. 1.

In the operation of the above-described device, energy applied to the horn I from the wave guide 23 propagates through the spaces between those of the fins I5 which lie in front of the mouth of the horn. When the rotor assembly 3 is in the position shown in Fig. 2, the energy i3 radiated in a somewhat divergent beam whose apparent source is approximately at the point 29 near the periphery of the scanning assembly at the center of the stack 1. The lens 5 collects and concentrates the radiated energy in substantially parallel rays, 'forming a fan-shaped beam which is narrow in the direction perpendicular to the ns I5 of the stack 1 but relatively wide in the direction parallel to said ns. It will be apparent to those skilled in the art that the beam may be made narrow both in elevation and azimuth by substituting for the horn I a radiator which is more highly directive in elevation.

As the motor 21 rotates the scanning assembly 3, for example clockwise as viewed in Fig. 2, the apparent source on the periphery of the rotor moves clockwise (downward in Fig. 2), causing the concentrated beam from the lens 5 to swing in the opposite direction, i. e., counterclockwise, or to the left. This continues until the last of the bundle 1 of ns has passed the mouth of the horn; then the first of the bundle I3 comes into play. At this time, the apparent source of radiation disappears from its lowermost position and reappears at its upper extreme position.

With continued rotation of the scanning assembly the apparent source repeatedly moves from left to right, starting at the left as each bundle of fins begins to pass in front of the radiator I. The beam from the lens 5 moves sawtooth fashion from right to left, jumping back substantially instantaneously to its starting position at the conclusion of each scan.

Although the operation has been described in terms of transmission of energy, the structure will operate also for reception, scanning repeatedly and providing output in the wave guide 23 whenever the beam points at a radiating source.

The described structure is particularly useful in conjunction with a radiator or collector which scans in a direction at right angles to the scanning provided by the rotor 3. Such radiators or collectors are well known.

I claim as my invention:

1. A scanning antenna system for polarized electromagnetic energy comprising a beam pattern forming directive radiator or collector, a plurality of groups of conductive sheets, the sheets of each group being in spaced parallel planes substantially normal to the direction of the electric vector of the polarized energy, and means supporting said groups for rotation around said radiator to pass in succession across the beam pattern of said radiator or collector.

2. The invention as set forth in the foregoing claim, including a focusing device in the path of said beam and outside the space swept by said sheets.

3. A scanning antenna system including a cross shaped member whose arms each comprise a stack of parallel sheets, a directive beam forming radiator for radiating polarized electromagnetic energy positioned substantially at the center of said cross, the planes of said sheets being substantially normal to the direction of the electric vector of the polarized energy, means rotating said cross shaped member about said radiator whereby said arms pass in succession across the beam of said radiator, and beam converging means outside said cross and in the path of said beam.

4. A scanning antenna system comprising a beam forming directive radiator for radiating polarized electromagnetic energy, an annular scanning assembly surrounding said radiator and intercepting the beam of said radiator, said assembly including at least one group of spaced parallel sheets extending in a generally radial direction from said radiator and substantially normal to the direction of the electric vector of the polarized energy, and means rotating said annular assembly about an axis through said radiator and parallel to said sheets.

5. The invention as set forth in claim 4, including means outside said scanning assembly and in the path of said beam for concentrating into a beam the energy owlng from said radiator through said scanning assembly.

HARLEY IAMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,075,808 Fliess Apr. 6, 1937 2,078,302 Wolf Apr. 27, 1937 2,283,568 Ohl May 19, 1942 2,442,951 Iams June 8, 1948 2,452,349 Becker Oct. 26, 1948 2,460,401 Southworth Feb. 1, 1949 OTHER REFERENCES Electronic Industries, page 66, March 1946. 

